This year, we continued to study the role of mismatch repair in regulating the genome-wide mutation rates of yeast cells harboring variant, proofreading-deficient alleles of the major leading and lagging strand enzymes, DNA polymerases epsilon and delta. These studies, which are being performed in mismatch repair proficient and deficient yeast cells, are well underway, but no publications have resulted. They should be informative regarding the roles of nucleotide selectivity, proofreading and mismatch repair to genome wide mutation rates for base substitution and insertion-deletion errors.